padding arrays using numpy

Question

in my program i have a numpy array and do some convolution filtering on it. i am looking for some way to make array padding (and then unpad for output) easily using numpy to avoid boundary checking. i know that scipy can do convolution, but i have reasons to make it by myself. gnuplot.py is used for output.

def touch(field, coords, value):
    field[coords[0], coords[1]] = value
    if coords[0] - 1 > 0:
        field[coords[0] - 1, coords[1]] = value / 2
    if coords[1] - 1 > 0:
        field[coords[0], coords[1] - 1] = value / 2
    if coords[0] < field.shape[0] - 1:
        field[coords[0] + 1, coords[1]] = value / 2
    if coords[1] < field.shape[1] - 1:
        field[coords[0], coords[1] + 1] = value / 2

Is that really convolution? That code will overwrite all neighboring cells, without regard to their previous value. What are you really trying to do? — Petr Viktorin
– Petr Viktorin, Commented Oct 8, 2011 at 15:05

Petr Viktorin · Accepted Answer · 2012-08-26 18:49:53Z

6

There's a pad module scheduled for inclusion in Numpy 1.7.0 – see this ticket. For now, just download it and use its with_constant function.

Unpadding is as simple as field[1:-1, 1:-1].

edited Aug 26, 2012 at 18:49

answered Oct 8, 2011 at 15:34

Petr Viktorin

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1 Comment

Hooked Over a year ago

If you want to edit the answer, padding is now live in 1.7.0. The doc link is here docs.scipy.org/doc/numpy/reference/generated/numpy.pad.html

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